Various types of mounts have been used to secure vehicle powertrain components, such as an engine, electric motor, transmission, etc. to the underbody structure of the vehicle. Mounts may include rubber or similar elastomeric materials to dampen or isolate various types of motion associated with the vehicle powertrain to reduce transmission to the rest of the vehicle, particularly the vehicle cabin where it may be perceived by vehicle occupants as noise or vibration. Mounts may include various materials or features that provide a desired frequency response and may be selectively tuned by design or actively controlled during vehicle operation to provide more attenuation or damping at frequencies associated with certain powertrain component operating modes, such as engine idling or lugging, for example. Other damping or stiffness characteristics may be used to provide desired performance for operating modes having different characteristic frequencies that may be associated with road surface conditions, engine or motor speed changes, etc.
Hydraulic, hydroelastic, or hydro-mounts are commonly used in passenger car applications and include a chamber filled with glycol or hydraulic fluid to isolate idle and part/open throttle powertrain excitations, as well as for controlling vehicle shake under road inputs. Depending on the particular application and implementation, designs may include passive hydro-mounts or actively controlled/switchable hydro-mounts. Switchable hydro-mounts may include an idle mode of operation that provides a reduction in stiffness at the frequency range of engine firing order excitations at engine idle speeds, and a shake mode that provides increased damping for large excitations while concurrently providing low dynamic stiffness for small amplitude excitations at higher frequencies (such as 20 Hz and above) through a decoupler. Switching between a default mode (ride or cruise mode, for example) and idle mode is typically achieved by applying vacuum to the rubber membranes including the decoupler of the hydro-mount using an associated control valve. However, various designs may provide unfavorable stiffness during operating modes when vacuum is not applied, particularly within frequency ranges associated with operating modes such as engine lugging, for example.